Technically pure cro2



R0 Drawing.

UNITED STATES CHAD H. HUMPHRIEfiOF INDIANAPOLIS, INDIANA, ASSIGNORINDIANA, A CORPORATION CORPORATION, OF INDIANAPOLIS,

" ul VEI IIUUIII PATENT OFFICE TOMETALS rnorucrron or INDIANA'rEcnNIcALLYrUnE cro.

Application filed March 3,

This invention relates to technically pure C10,; and it comprises as anew com osition of matter crude dry CrO containing 0 as an impurity andadmixed with a dry reactive barium compound, such as barium hydroxid orbarium carbonate, in amount corresponding to said S0,," all as morefully hereinafter set forth and as claimed.

Commercial chromic acid is chromium trioxid, CrO It is used in variousarts and particularly in making electrolytic baths for plating chromium.The usual bath for this .purpose consists of a solution of CrOcontairiing minor but definite amounts of Gr O and of S0 As chromium isplated out, replenishment is by addition of CrO In the factory CrO ismade by adding sulfuric acid to astron solution of a bichromate, usuallysodium iichromate, whereupon most of the 010, set free recipitates asred crystals in a mother liquid containing sulfuric acid and an acidsulfate; usually acid sodium sulfate. Dry commercial CrO is ordinarilymade by removing the mother liquor as completely as ossible and thendrying the .010, by heat. 11 so drying most of the retained sulfuricacid is fumed off. In so doing however there is a limit to thetemperature which can be used since the CrO tends to dissociate. Thelonger the heating or the higher the temperature, the more complete isthe removal of sulfuric acid but the greater the dan er of breakingupCrO, and making a pro uct not completely soluble in water. As actuallymade, technical CrO always contains residual sulfuric acid in someamount. And it may contain acid sodium sulfate as well. In ordinarygrades of CrO, the sulfuric acid may vary from 1.5 per cent SO to 0.15per cent. As noted however with low proportions of sulfuric acid thereis apt to be reduced CrO, present produced by overheating in 'n and thepreparation may be not comp ete y soluble in cold water.

For urposes where chemically pure (lrO is required the presence ofeither Cr O or of sulfuric acid is naturally ob'ectionable, and both areundesirable in Crb, used for replenishment of plating baths. Both mustbe present but be present in definite amounts in 165755- 4:

1928. Serial No. 258,993.

such a bath, and'additions of either are undesirable. If sulfuric acidoccurs in the replenishing CrO the SO," content of the bath builds upabove the desirable amount.

There is commercially available a purer grade of CrO termed C. laboriousand expensive process wherein the sulfuric acid in wet precipitatedcrystallized CrO made as above described is first displaced by a strongsolution of nitric acid (in which CrO is not very soluble) this being inturn displaced by a saturated water solution of CrO This C. P. grade ofCrO is however too expensive for all ordinary uses, and in particularfor replenishing chrome plating baths.

It is the purpose of the present invention to provide a simple and readymeans for producing chemically pure CrO solutions from crude technical01:0... To this end, the wet precipitated, crystallized CrO made in theordinary way is freed of mother liquor by suction or by a centrifugal ascompletely as possible and is then dried in heated pans in the usualway. In drying, most of the moisture and some of the sulfuric acid arefumed off. Where absence of sodium compounds is desired the motherliquor of the crystal magma may be displaced by sulfuric acid prior todraining. In drying the CrO the temperature is kept below that at whichthe CrO,

P. made by a rather will dissociate, so that the dried product 1 is allsoluble in cold water; The last traces of 80., ion. The dry mixture canthen be packaged and stored indefinitely. On placing in water, thebarium compound and the sulfuric acid react to form a precipitate ofinsoluble barium-sulfate which can be settled out or be filtered out ifnecessary or desired,

giving a clean, chemicall pure solution of chromic acid. Barium su fatebeing wholly inert as regards most chemical reagents the presence ofsuspended sulfate is often immaterial and in such cases simple settlingout of the bulk of the precipitate may be sufficient.

The composite preparation made as described can be prepared cheaply andgives pure CrO solutions on contact with water.

I find on the whole barium hydroxid is best adapted for my purposes.However, dry barium carbonate or barium chromate may be used. Bariumhydroxid and chromate have the advantage that in the event of access ofmoisture to the packaged material and any deliquescence of the CrO therewill be no evolution of gas as in the case of the use of bariumcarbonate.

For some purposes, as in chrome plating, as stated, a definite andascertained amount of sulfuric acid is desired in the bath. Where thereis any object in producing CrO for replenishment 'containin a low butdefinite c ontent of SO, ion, this can be done by addmerely enoughbarium compound to correspond with the excess of sulfuric acid above itthe desired maximum quantit For example, some users specify a Cr 8containing SO, in not more than 015 per cent.

preparation takin this exact amount of suly furic acid into so ution canbe readily pre- 5 the present invention. It is however simpler to addthe amount of barium carbonate corresponding to all the sulfuric acidpresent and let the user put the amount of sulfuric acid which he wantsin the CrO pared under solution he makes.

An excess of barium compound over and above the amount corresponding tothe SO"? ion is usually unnecessary and adds only to However, thepresence of the the expense.

excess does not interfere in most cases with the production of a C. P.solution of CrO,

since the excess barium carbonate forms insoluble barium chromate.

What I claim is 2- 1. As a new composition of matter for In testimonywhereof, I have hereunto affixed my signature.

CHAD H. HUMPHRIES.

making substantially pure solutions of CrO I on addition of water a drymixture of crude CrQ containing S6 ion as an impurity and a reactivebarium compound, said barium compound being present in an amountcorresponding to the amount of'SO," present.-

2. As a new composition of matter for making substantially puresolutions of CrO,'

on addition of water, a dry mixture of crude CrO containin SO, ion as anim urity and barium by roxid, said barium by roxid being present in anamount corresponding to the amount of SO," present.

3. In the roduction of pure aqueous solutions of Cra the process whichcomprises dry mixing technical GrO with a small quantity of a watersoluble dry barium com-

